1. Field of Invention
The invention relates to a method for direct functionalization of polyaniline and other molecules having at least one diiminoquinoid ring through C—C bond formation, and to a product yielded with the same method.
2. Description of Related Art
Addition reactions for the α,β-unsaturated carbonyl compounds via Michael addition reaction through the formation of a new C—C bond have been reported. While the similar Michael addition reactions for the α,β-unsaturated imino compounds or diiminoquinoid rings through the formation of a new C—C bond have not been successfully prepared and reported. Pan is known to be an important type of conducting polymer, which has diaminobenzenoid rings and diiminoquionoid rings in a certain ratio and has been renowned for its poor solution-processability in the absence of substituents on the rings.
Though the solubilities of substituted-polyanilines (S-Pans) prepared from alkyl- and alkoxy-substituted aniline monomers via the conventional oxidative polymerization or copolymerization method were found to be higher than the unsubstituted Pan, their conductivities were found to be ˜1-5 orders of magnitude lower than the unsubstituted Pan. The much reduced conductivities are believed to be caused by the increased extent of the non-conjugated defect backbone structures that was induced to form during the growth of the polymer chain due to the competing electronic directing placement effect of the substituent.
Such problem can be solved by using the concurrent reduction and substitution (CRS) reaction method to introduce substituents after the polyaniline backbone is made. For example, highly conductive and highly processable functionalized polyanilines with various alkylthio or alkylamino groups have been prepared via the CRS method by reacting a Pan of a desirable redox state with thiols or amines as nucleophiles. The reactions were believed to occur at the diiminoquinoid sites following a typical Michael addition fashion, which converted unsubstituted diiminoquinoid rings into substituted diaminobenzenoid rings, via the formation of a new C—S or C—N bond, respectively.
Although these alkylthio- and alkylamino-substituted polyanilines all showed clearly improved processability, they still suffered some disadvantages. For example, the alkylamino-substituted polyanilines in general show an order of magnitude lower conductivity than the unsubstituted-Pan, due to the fact that these newly introduced amino groups have relative higher basicities and would compete significantly with the polyaniline backbone for the protonic acid dopant, thus showing an adverse effect on the conductivity for the doped Pan. Although the alkylthio-substituted polyanilines do not show such adverse conductivity effect, the relative weak C—S bond and the oxidation-sensitive sulfide group would render the materials and possibly their application products with relative poor long-term stabilities. Thus, it would be highly desirable to functionalize Pan with an alkyl group via the CRS reaction route, because the alkyl group is not only less basic than an amino group, but also more stable against oxidation than an alkylthio group.
However, the efforts in extending the same addition reaction to carbon-based nucleophiles have however proved to be futile, up to now.